From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7137A3A9DA4; Mon, 9 Mar 2026 14:22:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773066155; cv=none; b=IN3Oluu9y6qqpwwBD+o+igwtKwLMcRnAR48BUtw4xqZOgIhMgqUBP0dV7n9b2yZvT97xlxxylztUMctuh4tezK4PZ9OcCh5OWcH2vHU2UCIAA7r7BSneoqhYAzHzQF83JhG5tZXtxoY3DgU5WRLlII/D3q6Gkp3SR+tL9+BNs6Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773066155; c=relaxed/simple; bh=5KlEfbz0Ee4iB8X6UNcKHVf2pxVqxGqjkSUK1qr0Ki4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=bL1g8tQD524L29PuRTBNSEZU6bWKRj4nKzNtuzQTl1Z3tKlhtS5m71m4svkLoex32nvPAAyK6yYxS0X+qJJze61UZK4T9LLCw8P37HOuXnYYY4Ci2E/p9Cemc/F4GVJgex9va0BPP7FulKp62OAD9UJHQySGOp+PNEStWRXAukw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=sAMSqI/u; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="sAMSqI/u" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1F3FEC4CEF7; Mon, 9 Mar 2026 14:22:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773066155; bh=5KlEfbz0Ee4iB8X6UNcKHVf2pxVqxGqjkSUK1qr0Ki4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=sAMSqI/uCvaejl/SUMKvoSWH6sSKm5gIS5a7zZC1gBP+slwLpC/zYJd9K6T2Li00b my7gQs9YzFHCkFHNeSo4WXKTjIdOzztCtEcIdwryUoOJpR7udIQN51pFPDwQhDlqU8 AVYjfJ3X63dHXNKTHVNtoG650ZchzyUZ2+f0pcaTVbptv7OVZNYoyZ4/K5pR17HnMT JBF/S4MvLr9HbP1i+lUbJ88WOiEauPQLtObsYtQ6Tg5brdOIp+TGxXI3/IxRb6Nyt9 iaOghqdSWK+HOdfh9/ca+HrpHCnyXv1o6C3Ba+0qDpwi/Qs42oZby+pXqkp4bcrRuN pqPISn1qnChiQ== Message-ID: Date: Mon, 9 Mar 2026 15:22:28 +0100 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] binfmt_elf: Align eligible read-only PT_LOAD segments to PMD_SIZE for THP To: WANG Rui , Alexander Viro , Christian Brauner , Jan Kara , Kees Cook , Matthew Wilcox Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260304114727.384416-1-r@hev.cc> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/4/26 12:47, WANG Rui wrote: > When Transparent Huge Pages (THP) are enabled in "always" mode, > file-backed read-only mappings can be backed by PMD-sized huge pages > if they meet the alignment and size requirements. > > For ELF executables loaded by the kernel ELF binary loader, PT_LOAD > segments are normally aligned according to p_align, which is often > only page-sized. As a result, large read-only segments that are > otherwise eligible may fail to be mapped using PMD-sized THP. > > A segment is considered eligible if: > > * THP is in "always" mode, > * it is not writable, > * both p_vaddr and p_offset are PMD-aligned, > * its file size is at least PMD_SIZE, and > * its existing p_align is smaller than PMD_SIZE. > > To avoid excessive address space padding on systems with very large > PMD_SIZE values, this optimization is applied only when PMD_SIZE <= 32MB, > since requiring larger alignments would be unreasonable, especially on > 32-bit systems with a much more limited virtual address space. > > This increases the likelihood that large text segments of ELF > executables are backed by PMD-sized THP, reducing TLB pressure and > improving performance for large binaries. > > This only affects ELF executables loaded directly by the kernel > binary loader. Shared libraries loaded by user space (e.g. via the > dynamic linker) are not affected. > > Signed-off-by: WANG Rui > --- > Changes since [v1]: > * Dropped the Kconfig option CONFIG_ELF_RO_LOAD_THP_ALIGNMENT. > * Moved the alignment logic into a helper align_to_pmd() for clarity. > * Improved the comment explaining why we skip the optimization > when PMD_SIZE > 32MB. > > [v1]: https://lore.kernel.org/linux-fsdevel/20260302155046.286650-1-r@hev.cc > --- > fs/binfmt_elf.c | 29 +++++++++++++++++++++++++++++ > 1 file changed, 29 insertions(+) > > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c > index fb857faaf0d6..39bad27d8490 100644 > --- a/fs/binfmt_elf.c > +++ b/fs/binfmt_elf.c > @@ -28,6 +28,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -489,6 +490,30 @@ static int elf_read(struct file *file, void *buf, size_t len, loff_t pos) > return 0; > } > > +static inline bool align_to_pmd(const struct elf_phdr *cmd) > +{ > + /* > + * Avoid excessive virtual address space padding when PMD_SIZE is very > + * large (e.g. some 64K base-page configurations). > + */ > + if (PMD_SIZE > SZ_32M) > + return false; > + > + if (!hugepage_global_always()) > + return false; > + > + if (!IS_ALIGNED(cmd->p_vaddr | cmd->p_offset, PMD_SIZE)) > + return false; > + > + if (cmd->p_filesz < PMD_SIZE) > + return false; > + > + if (cmd->p_flags & PF_W) > + return false; > + > + return true; > +} > + > static unsigned long maximum_alignment(struct elf_phdr *cmds, int nr) > { > unsigned long alignment = 0; > @@ -501,6 +526,10 @@ static unsigned long maximum_alignment(struct elf_phdr *cmds, int nr) > /* skip non-power of two alignments as invalid */ > if (!is_power_of_2(p_align)) > continue; > + > + if (align_to_pmd(&cmds[i]) && p_align < PMD_SIZE) > + p_align = PMD_SIZE; The function name does not make any sense when reading this chunk. "should_align_XXX_to_pmd" ? -- Cheers, David